Mobile IPv4 and other similar network-layer mobility protocols suffer an inherent drawback known as “detour routing.” See C. Perkins, “IP Mobility Support”, IETF RFC2002, October 1996, G. Montenegro, “Reverse Tunneling for Mobile IP, revised”, IETF RFC3024, January 2001 and R. Jain, et al., “Mobile IP with Location Registers (MIP-LR)”, IETF Internet Draft, July 2001. This phenomenon occurs when a visiting mobile host communicates with a host on a visited network, and is depicted schematically in FIG. 1 (where MH stands for Mobile Host, Web for Web server, RT for Router, and HA for Mobile IP Home Agent). For example, when the visiting mobile host 100 attempts to access a local Web server 102, all outbound IP packets are routed via RT 104 to the mobile host's home agent 106 over an intermediate network 107 using an IP tunnel (shown schematically as IP-in-IP packet 108, with the encapsulated inner packet identified at 110), regardless of the destination for these IP packets. The mobile host cannot directly send outbound IP packets to a destination host as regular IP packets using the mobile host's home IP address and the destination host's IP address (as the source and destination IP addresses, respectively), because the mobile host's home IP address may not belong to the visited network. Accordingly, these IP packets may be dropped by routers having a “source filtering” function, which is widely adopted as described in “Reverse Tunneling for Mobile IP, revised”, IETF RFC3024, January 2001. Therefore, if the destination host is on the visited network, IP packets from the mobile host are forced to travel round trip between the visited network and the mobile host's home agent 106. This doubles the traffic load on the visited network and all intermediate networks between the visited network and the home agent. It also has a negative impact on the performance of real-time networking applications running between the mobile host and the destination host due to long round-trip delay.